The invention relates to rear projection screens, and more particularly to a rear projection screen having reduced speckle.
Rear projection screens are increasingly being used for projection displays in, for example, televisions, computer monitors, and other types of displays. The major optical characteristics of a rear projection screen include optical gain, viewing angle, contrast, and resolution. It is also important that the screen be free from optical defects, such as Moirxc3xa9 patterns, and color and speckle defects. Speckle defects can occur when light transmitted by a particular portion of the screen is mutually coherent with light transmitted by a neighboring portion of the screen. The mutually coherent light from neighboring portions of the screen interferes as it propagates away from the screen. A viewer""s eye integrates such interference over the whole screen, with the result that the viewer sees a number of bright spots across the screen, referred to as speckle, which decrease the viewability of the image projected from the screen.
A measure of speckle is the speckle contrast, which is defined as the ratio of the standard deviation of the pixel brightness over the average pixel brightness. If the speckle contrast of a screen is above a certain level, the speckle in the viewed image can be significantly distracting to the viewer. Accordingly, it is important to reduce the speckle contrast to a level acceptable to the viewer while substantially preserving other screen characteristics.
When screens are designed to enhance one or more particular characteristic it is often found that other characteristics are spoiled, or the cost of the screen assembly, or its complexity, is increased. For example, the introduction a component to the screen for reducing glare may adversely affect one of the other screen characteristics, such as gain, resolution or speckle. Ideally, any measures taken to reduce speckle should affect the other screen characteristics as little as possible.
Therefore, there is a need to reduce speckle in rear projection screens while substantially maintaining the other screen characteristics, and without significantly affecting the overall cost or complexity of the screen assembly.
Generally, the present invention relates to a rear projection screen having one or more internal layers that reduce the speckle perceived by a viewer. One particular embodiment of the invention is a screen assembly having a light-source side and a viewing side. The assembly includes a screen layer to disperse light passing through the screen from the light source side and a matte surface disposed on the viewing side of the screen assembly to reduce ambient glare. A first speckle contrast reducing layer is disposed between the screen layer and the matte surface to reduce speckle formed at the matte surface.
Another particular embodiment of the invention is a screen assembly having a light input side and a viewing side. The screen assembly includes screen dispersing means for dispersing light propagating from the light input side of the screen assembly and glare reducing means on the output side of the screen assembly for reducing ambient glare on the output side of the screen assembly. First speckle reducing means are disposed between the screen dispersing means and the glare reducing means to reduce speckle formed at the glare reducing means.
Another particular embodiment of the invention is a projection system that includes a projection screen assembly having an input side and an output side. The projection screen assembly includes a screen layer to disperse light propagating through the screen assembly from the input side, a matte surface on the output side and a speckle contrast reducing layer disposed between the screen layer and the matte surface to reduce speckle at the matte surface. A light image source projects an image of light on to the input side of the screen assembly.
Another embodiment of the invention is a screen assembly, having a light-source side and a viewing side. The screen assembly includes an image-forming screen layer to disperse light passing through the screen from the light source side and a matte surface disposed on the viewing side of the screen assembly to reduce ambient glare. A first coherence reducing layer is disposed between the screen layer and the matte surface to reduce coherence of light passing from the screen layer to the matte surface.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.